Sizing of pulp with rosin and carboxymethylcellulose



Oct. 30, 1951 E. F. HQRSEY ETAL 2,572,932

SIZING OF PULP WITH ROSIN AND CARBOXYMETHYLCELLULOSE Filed May 11, 1946 2 SHEETSSHEET l VFIG.I

INK TEST SIZING NEWS IOO

O 20 4O 6O 80 I00 PER CENT SODIUM GARBOXYMETHYLCIZLLULOSE I00 80 6O 4O 2O 0 PER C-ENT ROSIN SIZE ELEA NOR F HORSE) DONNA PR/CE INVENTORH BY Sunni Q. W Lawn Oct. 30, 1951 E. F. HORSEY ET AL 2,572,932

SIZING OF PULP WITH ROSIN AND CARBOXYMETHYLCELLULOSE Filed May 11, 1946 2 SHEETSSHEET ,2

FIG. 2

INK TEST SIZING NEWS O 0.2 0.4 0.6 0.8 L0 L2 DEGREE OF SUBSTITUTION SODIUM CARBOXYME THYL GROUPS PER ANHYDRO-GLUCOSE UNIT ELEANOR E H0365) OOAI'A/A PRICE IN VEN TOR5 Patented Oct. 30, 1951 SIZING F PULP WITH ROSIN AND CARBOXYMETHYLCELLULOSE Eleanor vF. Horsey and Donna Price, Wilmington, Del., assignors to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application May 11, 1946, Serial No. 669,028

1 Claim.

This invention relates to an improvement in theart of paper sizing, and in particular concerns a method of increasing the sizing efllciency of rosin size. It further relates to new and improved sizing compositions.

Throughout the papermaking art, the most extensively employed method of sizing to impart water and ink resistance to the paper comprises adding saponified rosin size to the pulp suspension in the beater, or at some other point prior to formation of the paper web on the papermaking machine, and thereafter adding papermakers alum (aluminum sulfate) to cause the formation of a sizing precipitate on the pulp fibers. Many variations of this general procedure have been proposed, and a. wide variety of materials has been suggested to replace all or part of the rosin size for the purpose of securing better sizing. Many of such materials, however, do not increase the sizing efficiency to the desired degree and/or detract from other properties of the (dry basis) of sizing compositions containing varying proportions'of rosin size and sodium carpaper; e. g., bursting and tensile strength, folding endurance, porosity, stability to discoloration, etc.

It is accordingly an object of this invention to provide means for securing improved sizing efliciency in papermaking without detracting from other desirable properties of the paper. Another object is to provide means for increasing the sizing efliciency of various types of rosin size. A further object is to provide new and improved sizing compositions. A still further object is to provide a. material which may be used to improve the efliciency of rosin size without detractingirom the strength and stability of the sized paper. Other objects will be apparent from the following detailed description of the invention.

It has been found that the foregoing objects and attendant advantages may be secured by replacing part of the rosin size, which is ordinarily added to the pulp furnish, with a water-soluble salt of carboxymethylcellulose; e. g., sodium, ammonium, calcium, or potassium carboxymethylcellulose. Such salts have very little, if any, sizing value in themselves, but have the unusual property of greatly increasing the sizing efficiency of rosin size. Furthermore, in contrast to many other materials which have been suggested as rosin size additives, they do not detract from the strength of the paper, and, in fact, in many cases they actually increase the paper strength.

In the accompanying drawings, Fig. 1 illustrates the increase in sizing attained by replacing varying amounts of rosin size with sodium carboxymethylcellulose while maintaining the total boxymethylcellulose. The rosin size employed was a soda-cooked paste size prepared from gum rosin and containing about 20% by weight of free rosin, and the sodium carboxymethylcellulose has a degree of substitution of about 0.4; that is, it contained an average of about 0.4 carboxymethyl groups per anhydro-glucose unit.

The degree of sizing was determined by the well known news ink test which is described in detail in the Paper Trade Journal, vol. 105, pp. 363-370 (1937). Briefly, this test consists in measuring the time in seconds required for a standard ink composition to penetrate through a sample of paper undergoing test, the end point of the penetration being determined photoelectrically. Unless otherwise noted, all of the tests mentioned herein were made employing an light screen between the light source and the comparator photoelectric cell,

It will be readily seen from Fig. 1 that improved sizing efficiency is obtained when the carboxymethylcellulose salt is used to replace between about 3% and about 30% of the rosin size ordinarily employed. That is, improved sizing can be obtained without increasing the total amount of sizing solids by replacing from about 3% to about 30% of the rosin size with a water-soluble carboxymethylcellulose salt. On the other hand, if there isno objection to increasing the amount of sizing solids, improved sizing can be obtained by employing the carboxymethylcellulose salt in amounts up to of the rosin size. Thus, the sizing of a pulp sized with 2%, for example, of rosin size (based on the weight of dry pulp) can be improved by, the addition of up to 2% of the carboxymethylcellulose salt. The invention then contemplates the use of sizing compositions essentially comprising rosin size and between about 3% and about 50% of a water-soluble salt of carboxymethylcellulose. For economical reasons, however, it is preferable to limit the proportion of carboxymethylcellulose salt to between about 3% and about 20% of the total weight of the sizing ingredients.

Fig. 2 illustrates the relationship between degree of sizing and degree of substitution of the carboxymethylcellulose salt. This curve was plotted from data obtained in experiments similar to those described above in connection with Fig. 1,

but in this case the composition of the size was to a degree of between about 0.25 and about 0.70.

The principle or the invention thus lies in the use of rosin size and a water-soluble carboxymethylcellulose salt in the beater sizing of paper, the carboxymethylcellulose salt having a degree of substitution between about 0.25 and about 0.70 and beingemployed in an amount between about 3 and about 50, preferably between about 3 and about 20, per cent by weight of the combined rosin size and carboxymethylcellulose salt.

In applying the principle of the invention to practice, a number of different modes of operation may be followed. Ordinarily, however, the carboxymethylcellulose salt and rosin size are added to the pulp furnish in the beater or elsewhere at the wet end of the papermaking machine; e. g., at the stock box, Jordan engine, head box, or the like. The furnish is then treated with papermakers alum to a suitable pH, usually about 4.5, to precipitate the size on the paper fibers, after which the stock is diluted and run off on the machine in the usual manner. The carboxymethylcellulose salt may be added to the furnish either before or after the rosin size, and the alum may be added in any of the ways heretofore employed when using ordinary rosin size. The latter may be either a typical paste size, a high free rosin size in which a preponderating amount of the rosin is in unsaponified form, or a substantially neutral dry size.. Similarly, it may be prepared from any of the grades of wood or gum rosin or from wood or gum rosin which has been modified by heat-treatment, hydrogenation, polymerization, disproportionation or other treatment known in the art. If desired, various size additives, such as casein, soybean protein, waxes, and the like may be added. As hereinbefore stated, the carboxymethylcellulose is employed in the form of a water-soluble salt, preferably the sodium salt, having a degree oi! substitution between about 0.25 and about 0.70. It is conveniently added to the paper furnish as a dilute aqueous solution.

A very convenient method oi sizing in accordance with the invention consists in adding the rosin size and carboxymethylcellulose salt to the furnish at the same time in the form of a homogeneous mixture, and thereafter treating the furnish with alum and processing in the usual manner. Such mixed size compositions may take the form of paste sizes in which a predominant amount of the rosin is in saponifled form; they may be high free rosin type sizes, or they may be in dry form.

In preparing paste size compositions, the carboxymethylcellulose salt may be formed in situ by adding the requisite amount of carboxymethylcellulose to the rosin prior to its saponiilcation with soda ash, caustic soda, or other alkali. Thus, a mixture of G gum rosin, for example, and carboxymethylcellulose may be heated with sufllcient aqueous sodium carbonate to saponity 60-70% of the rosin and convert the carboxymethylcellulose to the corresponding sodium salt to form a typical paste size composition of, say,

70%solids content. Alternatively, such a composition may be prepared simply by stirring the desired amount of sodium carboxymethylcellulose into a previously prepared paste rosin size to obtain a homogeneous mixed composition. Such mixed paste sizes are employed in sizing in the same manner as previously known paste sizes; that is, they are usually diluted to a solids content of about 3% to 5% before being added to the pulp furnish. The dilution may be efiected simply by adding the thick paste to hot water with violent agitation, or more eiflciently, by mixing with a small quantity or hot water in an inJectortype mixing T tollowed-by further dilution with cold water.

Similarly, in preparing substantially neutral dry size compositions, for example, according to the general methodset torth'in U. S. Patent No. 2,134,911, the carboxymethylcellulose may be added to the rosin in the autoclave where'it is heated with a chemically equivalent amount of alkali under superatmospheric pressure and at a temperature of 275-375 F. until saponiflcation is substantially complete. The saponifled mixture is then discharged under pressure into a drying chamber, whereby it is instantly desiccated to form a light, dry, finely-divided powder consisting of substantially completely saponified rosin and an alkali-metal salt or carboxymethylcellulose. If desired, the usual antioxidants employed in dry rosin size compositions; e. g., phenyl-beta-naphthylamine, azobenzene, diphenylamine, p-phenylene diamlne, etc., may be incorporated in the composition in the usual manner. This type of composition may likewise be prepared simply by mechanically mixing a dry carboxymethylcellulose salt with commercial dry rosin size. They are usually added to the pulp furnish in the beater directly in dry form.

High free rosin type size dispersions comprising a water-soluble carboxymethylcellulose salt may be readily perpared merely by mixing an aqueous solution of the carboxymethylcellulose salt with the previously prepared rosin size dispersion. Inasmuch as carboxymethylcellulose itselI is a good dispersing agent. a portion of the casein or other stabilizing agent ordinarily employed in making high tree rosin dispersions may be omitted if desired. 1 g a The following examples will illustrate several ways in which the principle of the invention has been applied and will serve to demonstrate its applicability, but they are not to be construed as limiting the invention.

Example 1 This example illustrates the relation between the proportion of sodium carboxymethylcellulose employed in conjunction with a typical paste rosin size and the degree of sizing obtained. In each or the experiments tabulated below, a bleached sulflte pulp was beaten at a consistency of 2.5% to a treeness of about 750 cc. (Schopper- Reigler) Sodium carboxymethylcellulose having a degree of substitution of about 0.39 was then added to the beater in the form oi. a 1% aqueous solution in the amount specified in the table, and sumcient rosin size was then added to bring the sizing solids up to a total of 3.0% based on the weight of bone dry pulp. The rosin size was a commercial 70% solids paste size made from gum rosin, and contained about 20% of the rosin in free form. Prior to being added to the beater it was diluted to a solids content of about 3%. When the sodium carboxymethylcellulose and rosin size were well distributed throughout the pulp. papermakers alum was added as a aqueous solution to reduce the pH in the beater to about 4.5, thus precipitating the size on the pulp fibers. The stock was diluted to a consistency of about 0.25% with a solution of alum having a pH of about 4.5, and was then further diluted with water to a final consistency of about 0.025%. Handsheets were then run 011 on a Noble and Wood Laboratory papermaking machine, and were dried at 212 F. These sheets had a basis weight of about 39.5 pounds per 24 x 36 x 500 ream. The paper samples were conditioned at 75 F. and 50% relative humidity before being tester for porosity or air permeability on the Gurley densometer and degree of sizin by the news ink penetration test. The data are tabulated as follows:

Pesirgent 1 S 0 mm izmg Porosity Expt.No. (lllabggly- (Gurley) (gags cellulose Based on combined weight of rosin size and sodium carboxymethylcellulose.

Example .2

This example illustrates the relationship between the degree of substitution 01 the carboxymethylcellulose and the degree of sizing obtained. In each of the experiments tabulated below, a bleached sulfite pulp was sized in the beater and handsheets run off as in Example 1. In this case, however, the size composition was maintained constant at about by weight of sodium carboxymethylcellulose and 85% by weight of the paste rosin size while the type of carboxymethylcellulose was varied as regards its degree of substitution. The finished handsheets were 1 Average number of carboxymethyl groups per anhydro-glueose unit.

Example 3 A dry size composition was prepared by adding 50.5 parts of a 19.8% aqueous solution of sodium carboxymethylcellulose having an average degree of substitution of about 0.68 to 200 parts of molten rosin in an oil-jacketed autoclave. The mixture was heated to a temperature of about 162 C., after which 63.8 parts of sodium hydroxide in the form of a 39.6% aqueous solution were added. Heating was continued forabout minutes at a temperature of about 164 C. and under autogenic pressure, after which the reaction mixture was discharged into a chamber maintained at atmospheric pressure and at a temper- Example 4 A dry size composition similar to that described in Example 3 was prepared simply :by mechanically mixing 15 parts of sodium carboxymethylcellulose having a degree of substitution of about 0.39 with 85 parts of commercial dry rosin size. Paper samples prepared from pulp size in the beater with this composition had a news ink sizing test value of about 225 seconds, as compared to a value of about 138 seconds for a blank sample containing no sodium carboxymethylcellulose.

Example 5 A paste size composition was prepared by thoroughly mixin '75 parts of sodium carboxymethylcellulose having a degree of substitution of about 0.68 with 925 parts of a commercial soda-cooked rosin size containing about by weight total solids and about 20% by weight of free rosin. This sizing composition was a thick paste containing about 5.2% by weight of.

sodium carboxymethylcellulose on a dry basis. This composition was diluted with water to a concentration of about 3% solids, and was used in the beater sizing of a bleached sulfite pulp. Paper samples prepared from this pulp had a news ink sizing test value of about 233 seconds as compared to a value of 138 seconds for a blank sample containing no sodium carboxymethlycellulose.

Example 6 In the foregoing examples, the pulp employed was a bleached sulflte pulp. In order to demonstrate the applicability of the invention to various types of pulps, several diiferent pulps were sized in the heater and paper samples prepared according to Example 1. employed in an amount of 3.0% based on the weight of bone dry pulp, and consisted of 87% of a 70% solids paste rosin size and 13% of sodium carboxymethylcellulose having an average degree of substitution of about 0.39.

The news ink test sizing values of these paper 7 samples are tabulated below, together with comparative values on control samples containing no sodium carboxymethylcellulose:

1 50% screen employed in news ink test.

Example 7 The effect of freeness on the response of a given pulp to the increase in sizing attained through the use of carboxymethylcellulose salts in conjunction with rosin size was determined as follows: A bleached sulfite pulp was beaten The size wasv after sized in the beater with rosin size and sodium carboxymethylcellulose as in Example 8. vention is likewise applicable to furnishes comprising fillers, pigments, dyes, etc., in addition to the pulp. It is of particular value in sizing furnishes containing finely-divided fillers or pig- 1. The total sizing solids amounted to 3.0% ments since ash determinations on paper sambased on the weight of bone dry pulp, and the ples prepared from such furnishes show that usesodium carboxymethylcellulose was employed in of a carboxymethylcellulose salt in accordance amountof about 13.3% by weight of the total with the invention aids materially in retaining sizing solids. A paper sample prepared from such fillers or pigments in the paper web with this pulp had a news ink sizing value of about consequent less loss of filler or pigment in the 98 seconds as compared to 64 seconds for a machine white-water. In a similar manner, the blank sample containing no sodium carboxycarboxymethylcellulose aids in the retention of methylcellulose. Asecond paper sample prepared pulp fines in the web. in the same way from a pulp which had been As used herein and in the appended claims, th beaten to a Schopper-Reigler freeness of 825 [5 term rosin size" is employed in the sense undercc. had a news ink sizing value of about 205 stood in the art; that is, it includes liquid, paste, seconds as compared to 85 seconds for a blank or dry sizing compositions essentially comprissample containing no sodium carboxymethyling at least partially saponified rosin or modified cellulose. rosin, and which may contain additional stabiliz- As hereinbefore stated, the increase in sizing or modifying ingredients such as casein. 8 ying obtained through thp use of water-solubean protein, waxes, etc. ble carboxymethylcellulose salts in conjunction Other modes of applying the principle of our with rosin size in accordance with the ininvention may be employed instead of those exvention is attained with substantially no deplained, change being made as regards the methcrease in the strength of the paper. The data ods herein disclosed or the materials employed, tabulated as follows indicate that in most cases provided the step or steps stated by the following the improvement in sizing is accompanied by claim be employed, or the product defined by the an improvement in strength properties. These following claim be retained. data were obtained on a paper prepared from What we claim and desire to protect by Leta bleached sulfite pulp beaten to a freeness of ters Patent is: 750cc. (Schopper-Reigler) and sized in the beat- In th m thod f sizing p p pu p w i er according to the procedure described in Exrosin size is added to an aqueous suspension of ample 1. The paper was run off at a basis said pulp and papermakers alum is added thereweight of 40.0 pounds per 24 x 36 x 500 ream, after to precipitate the size solids upon the fibers, and was dried on the machine at 212 F. for '5 the improvement comprising adding a dilute 100 seconds. Before testing, the paper samples 1 aqueous solution of sodium carboxymethyl celluwere conditioned at 75 F. and 50% relative hulose to the aqueous suspension of said pulp prior midity. The rosin size was a 70% solids paste to the addition of alum, said sodium earboxysize containing 20% of free rosin. methyl cellulose having an average degree of sub- Sizing Dry Wet n Size 33;," 5.13125 53355 gg g g Znif ill? T 13, $233, Sec. lb'lsqil'li lbJsqj'l. lb./sq.1n. lb./sq.1n. gms. gIllS,

3.0% Rosin size 10s 41 29 15 17.4 3.4 46 3.0% Rosin size+0.05% sodium carboxymethyl cellulose, substitution=0.3l 144 5a 29 11 20.1 4.6 50 50 While all of the foregoing examples relate to the sizing of simple machine furnishes comprising only beaten pulp, the principle of the institution of about 0.45 and being employed in an amount of about 15% of the combined weight of rosin size and sodium car-boxymethyl cellulose.

ELEANOR F. HORSEY. DONNA PRICE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

